Exemplary embodiments of the present invention relates to a drive system for an electrical machine, having a control unit and a monitoring unit, which is independent of the control unit, and to a method for operation of an electrical machine.
German patent document DE 102 51 095 A1 discloses a method for operation of an electrical machine, having a drive system, in which an operating variable of the electrical machine and/or of the drive system is monitored. The permissibility of an actual torque of the electrical machine is checked, and a fault reaction is initiated if the actual torque is not permissible. The permissibility of the actual torque is preferably checked in such a way that a permissible torque is formed from a nominal torque and from predefined limit values for the nominal torque, with the actual torque being permissible if its discrepancy from the permissible torque does not exceed a specific magnitude. This method can be used to monitor an electrical machine which is used as a starter/generator or as a hybrid drive in a motor vehicle.
Exemplary embodiments of the present invention provide a drive system with a fast reaction rate and good data quality, as well as a method for its operation.
A drive system for an electrical machine, comprising: a control unit including a device that converts one or more incoming operating parameters of the electrical machine to an output value; a monitoring unit, which is independent of the control unit, wherein the monitoring unit includes a device that converts the operating parameters to a comparison value, and the conversion is carried out more quickly in the control unit than in the monitoring unit; and a comparator, which compares the output value or an intermediate value of the output value with the comparison value.
Exemplary embodiments of the present invention provide a control unit for the drive system has a device that converts one or more incoming operating parameters of the electrical machine to an output value. A monitoring unit has a device that converts these operating parameters to a comparison value. Accordingly, the conversion is carried out more quickly in the control unit than in the monitoring unit. Furthermore, a comparator is provided, which compares the output value or an intermediate value of the output value with the comparison value of the output value or of the intermediate value.
The control unit forms the output value quickly and independently of the monitoring unit. This leads to the drive system having a fast reaction rate. The rapid production of the output value by the control unit makes it possible to use the output value as a controlled variable for a fast-reaction control loop.
Faults in the formation of the output value can be identified by comparison of the output value with the comparison value which is formed in the monitoring unit. The quality of the output values is monitored. The check of the intermediate values allows the fault location to be located. In this case, the device which has received error-free data and has emitted erroneous data is understood to be the fault location.
The advantage of this solution according to the invention is that the control unit can operate quickly and the fault monitoring can operate slowly, without significantly restricting the fault monitoring in this way. In particular, this also allows inaccuracies in the output value caused by the rapid processing to be discovered. Because, of course, these inaccuracies do not occur in this form in the comparison value, which is formed slowly, they lead to a discrepancy between the output value and the comparison value. If this discrepancy between the output value and the comparison value exceeds a specific tolerance band, then a fault is identified. It is therefore possible to check that the output value is correct.
In one aspect, the monitoring unit has a comparator, which compares a value formed from a value of the control unit in a device with a comparison value formed in a device of the monitoring unit. This makes it possible to identify faults in the formation of values by the control unit.
For example, an actual torque which is calculated from current components and from the information from a temperature sensor can be compared with an actual torque calculated from the same current components and from theoretical temperature values stored in a computer. This allows errors in the torque calculation to be identified. For example, it is possible to identify when the result of the torque calculation in the control unit is always incorrectly a zero torque. It is likewise possible to identify when the detected temperature values differ to a major extent from the theoretically expected values.
For example, an actual torque which is calculated from current components and from theoretical influencing variables stored in a computer can be compared with permissible limit values of the actual torque. This allows identification of errors in the torque calculation. It is then possible to identify when the result of the torque calculation is outside the permissible limit values.
In one aspect, the comparator identifies a fault when the output value which is supplied to it, the intermediate value of the output value or the value formed in a device is outside a tolerance band of the comparison value supplied to it. This makes it possible to permit minor discrepancies which are caused by the different calculation of the comparison values. Major differences which can be caused only by errors in the process of determining the values are in contrast identified as faults.
In one aspect, in the event of a fault, the comparator acts on an output stage of the electrical machine. For example, the output stage can be switched off or shorted. This prevents incorrectly calculated output values of the control unit from incorrectly driving the output stage. This prevents possible damage to the electrical machine. Impermissible torque formation is likewise prevented.
In one aspect, in the event of a fault, the comparator blocks the fault reaction of another comparator. This prevents a fault in one comparator leading to fault reactions in subsequent comparators, due to consequential errors. Since the fault reactions of other comparators are blocked, this ensures that the only comparator which produces a fault reaction is that in which a fault was initially identified. It is therefore possible to determine the source of a fault. This is important information for determination of the cause of the fault.
In one aspect, the output value is an actual current component for closed-loop control of an electrical machine. A control loop can therefore be described for control of the electrical machine. In this case, current components of the electrical machine are detected, converted and checked for errors in comparators. The actual current component calculated in this way is then provided as an output value from a closed-loop control system. A quickly calculated actual current component can therefore be made available to the closed-loop control system, which nevertheless is highly reliable, because it has been checked in a comparator.
In one aspect, the output value is a nominal current component for closed-loop control of an electrical machine. This allows a nominal current component to be made available for closed-loop control, which is calculated and output quickly and is nevertheless highly reliable because it has been checked in a comparator.
The method for operation of an electrical machine having a drive system detects operating parameters of the electrical machine in the control unit and in the monitoring unit. The detected operating parameters are converted to an output value in the control unit. According to the invention, the detected operating parameters are converted to a comparison value in the monitoring unit. In this case, the conversion in the control unit is carried out more quickly than in the monitoring unit. The output value or an intermediate value of the output value is compared with the comparison value.
This makes it possible to identify errors in the formation of the intermediate values and in the formation of the output value. If a plurality of comparators are provided, then the fault location where the fault initially occurred can be determined. For example, it is possible to determine the device in which the fault initially occurred. It is likewise possible to determine the nature of the fault.
In one aspect of the method, a fault is identified when the output value or the intermediate value of the output value is outside a tolerance band of the comparison value. This tolerance band prevents minor discrepancies in the values to be compared being interpreted as faults, and initiating a fault reaction. The reason for such minor discrepancies may lay in the different computation rate and computation accuracy of the devices in the control unit and monitoring unit, and may therefore be unavoidable. The tolerance band ensures that only sufficiently large discrepancies from the comparison value are identified as faults. This improves the fault identification quality.
In one aspect of the method, in the event of a fault, an output stage of the electrical machine is switched off or shorted. This results in a safety shutdown of the electrical machine, thus ensuring that the electrical machine does not receive any incorrect or impermissible control commands in the event of a fault. The electrical machine is protected against damage, and impermissible torque formation is likewise prevented.
In one aspect of the method, in the event of a fault, an actual torque of the electrical machine is set to an implausible value. This implausible value is preferably a value which is not critical for the electrical machine. For example, the torque is set to an extreme value which is defined as being impermissible and must not be used during normal operation. This can then lead to a fault being identified when the actual torque is compared with the corresponding permissible limit values of the actual torque, or to a safety shutdown of the electrical machine.
In one aspect of the method, in the event of a fault, the fault reaction of another comparator is blocked. It is therefore possible to associate the fault with a comparator which has initiated the fault reaction. This makes it easier to identify the cause of the fault.